This invention relates generally to fiber amplifier arrays and, more particularly, to techniques for controlling the phase relationships of multiple emitters in a phased array of fiber amplifiers. Fiber amplifier arrays have been used or proposed to provide a high power optical source. Basically, the optical outputs of multiple fiber amplifiers in an array can be effectively combined to produce a high power beam if the phases of the individual amplifier outputs are controlled to provide a coherent composite beam.
Various methods have been proposed for controlling the phase of each emitter in a phased array of fiber amplifiers. Prior to this invention, the most successful of the methods involves measuring the phase of each emitter and adjusting the phase to produce a diffraction limited beam from the beam combining aperture of the array. An alternative scheme is to measure on-axis, far field power of the output beam and to provide a phase correction to each emitter to optimize the on-axis intensity of the beam. Another approach is to use analog heterodyne phase-locking techniques to lock the phase of each emitter to the phase of a master oscillator. The control systems needed to achieve phase control of the individual emitter outputs are effective in some of these approaches, but are also relatively complex and expensive to implement.
Therefore, there is still a need for a simpler and less expensive technique for coherently combining the outputs of multiple fiber amplifiers. The present invention satisfies this need.